A mountain bike (MTB) or all-terrain bike (ATB) is a bicycle that is designed for off-road cycling where there is no man-made road surface. Mountain bikes evolved from both road bicycles and from off-road motorcycles. One view is that mountain bikes are road bikes that have been adapted to handle the more difficult and demanding off-road terrain. Another view is that a mountain bike is a lighter and human powered version of an off-road motorcycles (without motor), designed to reach those off-road areas that are inaccessible to off-road motorcycles (e.g. due to regulation and otherwise).
Since the development of early mountain bikes in the 1970s, many subtypes have developed, including cross-country (XC), freeride, downhill, and various track and slalom mountain bikes. Each places different demands on a mountain bike with the result that specialised designs and components have emerged to cater for each subtype.
For example, mountain bikes designed for downhill events have evolved with much stronger, but heavier components; a typical downhill mountain bike weighs about 18 kg (40 lbs). It is thought that many such downhill components have been adapted from off-road motorcycles. One particular example is the wheel axle used by downhill mountain bikes. The downhill mountain bike axle is subjected to very high operating stresses due to the high speed and terrain induced impacts to which the bike is subjected. Due to the severe operating stresses, the downhill bike axle is very similar to a motorcycle axle, being comparatively large in diameter (e.g. 20 mm or 30 mm) and heavy in construction to provide strength and rigidity, and is usually rigidly fixed to the mountain bike by bolts that require tools for removal.
In contrast, cross-country mountain bikes have evolved with much lighter components; a typical cross-country mountain bike weighs about 12 kg (26 lbs). Many cross country components have been adapted or borrowed from road bikes, where the requirement for lightness is paramount. One particular example is the 9 mm quick release mechanism used to attach the front and/or back wheel to a mountain bike. The cross country mountain bike benefits from the light weight and quick release (for quick race condition tire changing and fixing) features of such a road bike wheel fixing mechanism. That road bike component has been used almost “as is” on mountain bikes, despite the fact that an off-road surface typically subjects a mountain bike to much higher stresses than are typically encountered in road biking.
While cross country mountain bikes benefit from the quick release and light weight features of a hub skewer such as a 9 mm quick release, that road bike derivative system lacks the rigidity of the downhill bicycle axle system. As such cross country mountain bikes handle less precisely in difficult terrain because they tend to flex more and particularly in the front end. Additionally, while the axles used on downhill mountain bikes augment fork stiffness, which can lead to improved control and ride quality, they are too heavy and difficult to work with in cross country applications. One problem with using downhill mountain bike axles on cross country mountain bikes is that, traditionally, downhill mountain bike axles require tools and time to remove them from the bike and they are not capable of quick release. This is because a downhill ride is typically very short (e.g. like a downhill ski run, a number of minutes) in comparison to a cross-country ride (e.g. a number of hours) and there simply is no need to be able to remove and replace a wheel quickly. In contrast, the ability to remove and replace a wheel as quickly and as easily as possible is of the upmost importance in cross-country mountain biking.
U.S. 2005/0110335 (the '335 application) discloses an axle assembly for connecting a wheel assembly to a bicycle front fork. The axle is provided with longitudinal slots at either end. A quick release skewer and cam assembly is used to move expansion elements, or “washers” into engagement with the axle so that the slotted sections are caused to expand radially against an inner diameter of the fork. A nut (or “acorn” nut as it is sometimes known) is at the opposite end of the skewer from the cam assembly. Thus, and disadvantageously, two hands are required to tighten and release the axle assembly. Therefore, the axle of the '355 application is used in a fashion very much like a standard quick release skewer. Specifically, the lever is held stationary while the nut is rotated to suit.
The axle of the '355 application, in for example paragraph 0026, includes open ended slots 25 in the axle body to facilitate radial deformation of the axle. Such slot or slots subvert the rigidity of the axle and may ultimately lead to early fatigue failure due to differential flexure (both axially and torsionally) of the axle material adjacent opposing sides of the slots (e.g. causing crack propagation from the apex of the slot). That is particularly likely regarding light weight axle materials such as aluminium. Such effect may be further exacerbated by the repeated radial expansion and relaxation, during installation and removal, of the axle “tabs” created by the slots. Such expansion and relaxation as effected by the expansion washers in repeated use amounts to cyclic bending of the “tabs.” Due to the high, and relatively long duration, cyclic loading placed on a cross country mountain bike axle, built in stress risers such as those included in the '355 application are not desirable.
Further, depending on the user's adjustment of the expansion washers and the swage angle included thereon, it is possible, and in some circumstances likely, that the expansion washers will become “stuck” in the axle ends due to over-tightening. Such sticking completely subverts any quick release benefit that may have otherwise been realized.
Thus there is a need for an improved quick release which combines the stiffness and durability properties of downhill-type axles with the fast release properties of cross-country quick releases.